The purpose of this proposal is to examine the control of pharyngeal collapsibility in both adults and children with obstructive sleep apnea. The major focus of this work is to determine whether specific mechanical or neural alterations cause increased pharyngeal collapsibility in adults and children with obstructive sleep apnea. In our recent work, we have been able to quantitate differences in pharyngeal collapsibility which account for varying degrees of airflow obstruction during sleep along a continuum of health to disease. In the current proposal, we will continue to employ a Starling resistor model of the upper airway to characterize the critical pressure (Pcrit) of the upper airway which is the major determinant of collapsibility. In Specific Aim 1, we will determine how age affects the structural and neuromuscular determinants of upper airway collapsibility in patients with apnea compared to those at risk for developing apnea (normal snorers). In Specific Aim 2, we will determine how neural activation of the genioglossus muscle influences collapsibility in the presence and absence of generalized neuromuscular activity. In Specific Aim 3, we will examine the mechanism by which neural activity in specific upper airway muscles modulate responses in collapsibility to specific structural alterations.Both human and animal experiments have been designed in a complementary fashion. Standardized recording techniques will be used for measurements of sleep, pressure, and flow. Novel techniques will be employed to stimulate specific muscles to determine the passive properties of the upper airway. The results of these studies have potential implications on the detection and treatment of disease.